ASTM D6378 Determination of Vapor Pressure of Petroleum Products
ASTM D6378 Standard Test Method for Determination of Vapor Pressure (VPX) of Petroleum Products, Hydrocarbons, and Hydrocarbon-Oxygenate Mixtures (Triple Expansion Method)
12. Procedure
12.1 Set the sample introduction temperature of the measuring chamber between 20 and 37.8°C.
12.2 Set the vapor-liquid ratio to the desired value X:1 (for test results related to Test Method D 5191, set the vapor-liquid ratio to 4:1).
12.3 Connect an aliquot of sample either in a syringe, pressurized sample container, or a tubing immersed in the sample to the inlet of the apparatus. Make provisions to avoid loss of high volatiles in the sample. The overall volume of the sample shall exceed the volume of three rinsing cycles plus the final test volume. Follow the manufacturer's instructions for introducing the test specimen into the measuring chamber.
12.4 Perform the three rinsing cycles (see 9.3) immediately after connecting the sample.
12.5 Introduce the test specimen into the measuring chamber by a stroke of the piston. The volume of the specimen shall be such that after the expansion to the final volume the programmed vapor-liquid ratio is achieved.
12.6 Close the inlet valve, and make the first expansion by a stroke of the piston.
12.7 Monitor the TPX every 20 +/- 2 s. When three successive readings agree within 0.1 kPa, record this resulting total pressure as TPX,1.
12.8 Make the second expansion, and monitor the TPX every 20 +/- 2 s. When three successive readings agree within 0.1 kPa, record this resulting total pressure as TPX,2.
12.9 Repeat 12.8 for the third expansion, and record the resulting total pressures as TPX,3.
12.10 Allow the temperature of the measuring chamber to increase to within 0.1°C of the desired test temperature. Monitor the TPX every 20 +/- 2 s. When three successive readings agree within 0.1 kPa, record this resulting total pressure as TPX,t.
12.11 Check for Sample Separation - After introducing the test specimen into the instrument for analysis, check the remaining sample for sample separation (see 8.4)
